Lifting devices associated with machinery including fixed location machinery as well as mobile machinery have existed for many years. Representative lifting devices are shown in U.S. Pat. Nos. 3,936,339, Geis, et al, 4,396,334, Sugimoto, et al, 4,645,408, Mizuno, and 4,685,861, Huetsch.
The Geis, et al patent shows a vehicle with forks 13 forming a platform which can be raised and lowered. The angular relationship of these forks to the ground is adjusted by means of hydraulic cylinders 12. This patent shows a platform lifting device which may maintain a parallel relationship to the ground, but requires adjustment of the hydraulic cylinder to maintain any particular angular relationship between the platform and the ground surface.
The present invention in a first embodiment provides a lifting device which automatically maintains a constant (typically parallel) relationship between the platform and the surface which the mobile base contacts.
Typically, the lifting device is mounted to a mobile base so that the plane of the platform is parallel to the surface upon which the mobile base rests. In this way, the present invention is able to maintain a parallel relationship between the platform and the surface upon which the mobile base contacts throughout the entire articulated movement of the lifting device.
In another embodiment, this constant relationship can be altered so as to allow the platform to be angularly articulated with respect to the surface contacting the mobile base. In this embodiment, the platform can be maintained in a level orientation so as to allow the platform to hold open fluid vessels or other objects level as the mobile base moves over sloped surfaces. This embodiment also allows for angular articulation of the platform so as to facilitate lifting and releasing objects such as pallets without translation of the platform or mobile base.
The present lifting device does not use nor require pneumatic control of the platform, but rather uses two arm assemblies with associated gears and shafts so as to automatically adjust the platform throughout the entire articulated movement of the lifting device. The arm assemblies also interact with each other so as to allow placement of the platform over the mobile base when the lifting device is in a home position and to extend the platform outward from the mobile base as the platform is moved to a lower extended position.
U.S. Pat. No. 4,396,344, Sugimoto, et al shows a pick and place type industrial robot having a forearm 22 with pivotal movement as shown in FIGS. 5, 6 and 7 thereof. Although a fixed orientation is maintainable between wrist 33 and the surface upon which the industrial robot is mounted, it maintains a desired orientation through means of either linking bars 47 (see FIGS. 9A and 9B thereof) or rotatable discs 41a and 41b as shown in the embodiment shown in FIGS. 10A and 10B. This reference also does not show or suggest a lifting device with two arm assemblies in combination with means for altering the angle of the platform so as to maintain the platform level while the mobile base moves over inclined surfaces, or at other times when such angular articulation is desired.
Also shown in the Sugimoto, et al patent are various prior art lifting devices, (see FIGS. 1 through 4), none of which suggest the use of arm assemblies with associated gears and shafts for maintaining a fixed angular relationship between a platform and the surface upon which a mobile base is placed.
The Mizuno patent illustrates a robot hand having a linkage system including an endless chain and a correction lever so as to compensate for uncontrolled angular displacement of the robot hand resulting from expansion or contraction of the robot hand shifting linkage. This reference does not disclose or suggest use of arm assemblies with associated gears and shafts as disclosed in the present invention for maintaining a given angular relationship between a platform and the surface upon which a mobile base is placed regardless of the articulated movement of the lifting device. It also does not show or suggest the angular articulation of the platform using such arm assemblies so as to maintain the platform level over an inclined surface.
Finally, the Huetsch patent discloses an industrial robot having mechanical links of a shoulder, arm and hand, joined in series with a waist joint, shoulder joint, wrist roll joint, and wrist pivot joint as well as a clutch mechanism associated with each joint. Although shafts and gears are used to drive the various joints, no suggestion is made of arm assemblies with associated gears and shafts so as to maintain a platform in a fixed angular relationship to the surface upon which the device is mounted throughout the entire articulated movement of the lifting device, nor of angular articulation of platform with respect to an inclined surface so as to maintain the platform level while the mobile base travels over such surfaces.
Other prior art are lifting forks associated with fork-lift type vehicles. Although such lifting forks maintain a parallel relationship with the floor surface upon which the fork-lift contacts, they do not maintain a parallel relationship to the floor surface by means of arm assemblies with associated gears and shafts. Indeed, the motion of such lifting-forks is typically in a vertical plane only, unlike the present invention wherein the articulated movement of the device encompasses two-dimensional movement of the platform.
Finally, the platforms associated with various work platforms used in industrial environments are typically hydraulically controlled and do not suggest use of two arm assemblies with associated gears and shafts for maintaining a fixed angular relationship between the platform and the surface upon which an associated mobile base is placed.
The present lifting device comprises first and second arm assemblies with associated gears and shafts and three joining members. The first arm assembly is pivotally mounted to the base plate of the mobile base and is capable of being angularly rotated from a home position wherein the platform is positioned over the mobile base to a lower extended position wherein the platform is positioned away from the mobile base. Throughout the articulated movement between the home position and the extended lower position, a parallel relationship is maintained between the platform and the surface upon which the mobile base is placed. The shafts associated with the first and second arm assemblies are rotated by the gears throughout this articulated movement in a manner so as to maintain this parallel relationship of the platform. Furthermore, the angular relationship between the first and second arm assemblies is restricted so that when this angle equals a predetermined value, the two arm assemblies contact each other. Such contact allows the platform to be placed over the mobile base when the lifting device is in the home position. None of these structural features are found or suggested by the prior art.
The second embodiment of the present invention incorporates a motor driven worm and gear so as to adjust the angular orientation of the platform without simultaneous movement of the arm assemblies. The worm can be interfaced to an inclination sensing device, such as a damped pendulum, to thereby adjust the angular orientation of the platform and maintain it level as the mobile base traverses an inclined surface.
The end result is a lifting device which is particularly adapted for use on mobile bases so as to provide the means for loading and unloading objects on the platform in an efficient and straightforward manner. By placing the platform over the mobile base, the lifting device also facilitates movement of loads by maintaining a combined stable center of gravity.